SU975807A1 - Process for producing spheroidal graphite cast iron - Google Patents

Description

The invention relates to foundry, in particular to the issue of obtaining high-strength iron.

A method of obtaining nodular cast iron, including sequential modified its magnesium-containing master alloys and graphitizing additives 01 Y

The closest in technical essence and the achieved effect is a method of manufacturing nodular castings _ν consisting in modifying pig iron by carburizing and maintaining a residual magnesium content of '0.04% by treating the pig iron with magnesium-containing reagents, pretreating the melt with ferrosilicon and final modifying the ferrosilicon powder immediately before pouring form £ 2y

The known method allows you to consistently receive castings with spherical

2

the form of graphite, in particular, in the production of thin-walled casting. However, as a rule, in real castings there is always the presence of both thin and massive joints. Massive sections are formed last and have lower strength characteristics compared to the thin parts of the casting. Two-step modification of the melt by ferrosilicon after it has been treated with magnesium-containing reagents does not ensure the required water density and strength characteristics in castings, since large inclusions of spherical graphite and a large number of non-metallic inclusions, black spots and other harmful impurities form in massive sections that crystallize last.

In addition, the known method is not

ensures the preservation of the effect of globularization for more than 15 minutes, which is 975807

leads to a dramatic change in the properties of the metal, if you fill the molds for this or a longer period of time,

The aim of the invention is to develop a method of producing nodular cast iron, which provides the extension of the effect of modification, increasing the water density and strength characteristics of the metal.

This goal is achieved by the fact that according to a known method of producing nodular cast iron, including smelting of steel low-silicon metal waste and cast iron return, carburizing the melt, treating it with magnesium-containing reagents, step-wise modifying during the processing with a graphitizing modifier with the melt with the melt, melt with reagents, step-wise modification of the process with a graphitizing modifier with the melt with the melt with a melt, reforming it with the melt-containing reagents, modifying with the blown melt with the air, using the pattern with the melt with air, the application, the application, the application, the application, the current application, has already been used. consistently until complete dissolution of each of them, and first enter 70-80% of the total consumption ligatures, then 60-70% of the total consumption of the graphitizing reagent, after which the remainder of the magnesium-containing and graphitizing reagent is injected.

The technological process of producing nodular cast iron according to the proposed method. It contributes to the extension of the effect of modifying, increasing the water density and strength characteristics of the iron. This is explained by the fact that significant losses of reagents introduced into the metal are associated not so much with waste and mechanical losses, as with their interaction with harmful metal impurities.

When the iron is modified, desulfurization, degassing and other processes occur simultaneously. Therefore, the dosage of magnesium-containing reagent is determined by its consumption of these processes, mainly on the connection with sulfur. With an insufficient amount of residual magnesium, mixed or vermicular graphite is formed, and with an excess of plastic or full chill. When treating cast iron with magnesium-containing reagents, there is also the danger of the formation of a characteristic defect of nodular cast iron, so-called “black spots”.

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The initial input of magnesium containing reagent in the amount of 75-80% of

its total consumption leads to effective desulfurization of the metal, refining of it, and blowing air contributes to the uniform distribution of the introduced reagent volume and refining of the melt. In addition, due to this, graphitization in the liquid phase contributes to the growth of graphite of a compact, partially spherical form, while eliminating the danger of the formation of “black spots”.

15 Using less than 75% of the total consumption of a magnesium-containing master alloy is ineffective, and using more than 80% leads to the slagging of the metal mirror and the subsequent entry

20 graphitizing reagent is difficult.

Entering 60–70% of the total consumption of a graphitizing modifier, for example, FS-75 ferrosilicon, helps accelerate graphitization, deoxidize the melt, which favorably affects the growth of graphite in the desired form and, moreover, to reduce magnesium carbon loss. With the introduction of modifying

Zo reagent immediately after the termination of the> reaction of the magnesium-containing ligature melt in the iron stabilized magnesium carbides, spherical and compact form of graphite. Magnesium carbides

35 at high temperatures, unstable and decay at high speeds. For the complete graphitization of graphite, the remaining amount (2025%) of magnesium-containing ligature is introduced.

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When a graphitizing reagent is introduced less than 60% of its calculated amount, the graphitization process is weak, increases the magnesium burnout, and exceeding it more than the upper limit coarsens the shape of graphite and increases the size of the globules. Further input of the remaining amount of magnesium-containing reagent contributes to the complete globularization of graphite, increases the number of globules and reduces their size, which positively affects the increase in the strength characteristics of cast iron. Subsequent modification of the melt with the remaining amount of ⁵⁵ grading reagent leads to a significant increase in the water density of the metal and prolongs the modifying effect. This is due to the fact that

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5 975807

by increasing the centers of graphite formation and increasing the release of graphite in the liquid state, the magnitude of the pre-expansion of the iron is reduced by 1.8-2 times. The melt blown, treated with globularizing and modifying reagents, is purged during all cycles of reactants injection. This helps to clean the melt from suspended impurities, 10

which, due to mixing, partially float up and are removed to the slag, and partially carried to the exhaust probe.

An example. The steel metal waste is melted with the subsequent casting of the following composition,% by weight: carbon 3.7; silicon 0.4 ', manganese 0.4; phosphorus 0.04; sulfur 0.03 in the MGP-102 induction furnace with a capacity of 150 kg. At 1400 ° C, the melt is poured into the casting ladle, in the bottom part of which there is a porous plug, where the air purge line is fed. When air is blown, its pressure exceeds the pressure of 25 pillars of metal by 0.6 MPa.

Simultaneously with the metal, 2% (75% of the total amount) of magnesium-containing ligature of the following composition is injected into the metal mirror: 8% magnesium, 30 52% silicon, 3% rare-earth metals, and the rest is iron. After the cessation of the pyroelectric effect, 1% (67% of the calculated amount) of FS-75 ferrosilicon is injected. After its assimilation by the melt, 0.5% of magnesium-containing master alloy is added.

After assimilation of this additive, 0.6% FS-75 is introduced. The total time of this technological cycle is 5 minutes. The melt temperature decreases by 30 ° C. The melt is poured samples for mechanical testing and fluid density. The effect of modification is assessed by withstanding the metal in. bucket, pouring samples every 5’min.

According to a known method, liquid iron is treated with a magnesium-containing ligature to a residual magnesium content of 0.035% in it, after which two-step modification of FS-75 by ferrosilicon is performed.

The table shows the properties of cast iron, processed by known and proposed methods.

The expected economic effect from the introduction of the method by increasing the strength properties of cast iron by 1, 2-2 times (tensile strength - 1.2 times, impact toughness - 2 times), water density 1.4 times and extending the effect of modifying to 25 minutes will be by preliminary calculation about 105 thousand rubles. in year.

The method of producing iron The limit is clear Shock Water trap Cooling time on viscosity but effect of jerk kgf / mm Ok, kgf / cm kgf / cm * , min *

Famous

50.4 3.8 76-78

15

Proposed

62.5 7.6 108-112

25

^ After the specified time, the amount of nodular graphite in the iron becomes less than the lamellar.

Claims (1)

Claim/ A method of producing nodular cast iron, including smelting ⁵⁰ steel low-silicon metal waste and cast iron return, carburizing the melt, treating it with magnesium-containing reagents, stepwise modifying during processing with a graphitizing modifier with melt blowing with air, characterized in that In order to prolong the effect of modification, increase the water density and strength characteristics of the metal, the introduction of magnesium-containing and graphitizing reagents is carried out successively until complete dissolution of each of them with the introduction of first 75-80% of the total consumption of magnesium-containing ligature, then 60-70% of the total consumption of graphitizing reagent, after which impose the rest if 7 The quantity of magnesium-containing and graphitizing reagents.